Present efforts in the field of electronics continues to place a premium on component size. Component miniaturization affords consumers with heightened levels of convenience. As a result, electronics manufacturers continue to seek ways to make electronics components smaller, leading to the production of more compact appliances, stereo equipment, medical implanted devices, etc. In addition, the requirements of military and space devices include smaller size, higher energy density, and reduced overall weight.
However, there are many factors limiting how small a component can be. For example, the technology of making capacitors used in components is limited by the availability of dielectric materials which can reliably hold and deliver a required charge, and withstand a required voltage while being extremely thin. Presently, an assortment of crystalline dielectric materials are incorporated into capacitors. Presently available crystalline compounds used as dielectrics in capacitors include, barium titanate, tantalum oxide, and an assortment of various polymeric and liquid crystal mixtures.
Capacitors are devices that store electrical energy. They typically consist of a dielectric material sandwiched between electrically conductive materials. A wide variety of capacitor configurations is possible. The performance parameters of a capacitor depend on the electrical characteristics of the materials selected, including the characteristics of the dielectric material. Such characteristics include dielectric constant, breakdown strength, resistivity, loss on dissipation factor, inductance, etc. Capacitor performance also depends upon the physical, mechanical, thermal and other properties of the materials used to make the capacitor.
Specialty electronics often require specially designed capacitors. In instances where electronics miniaturization is essential, there is a need to reduce the volume of the capacitor, and a need to increase the capacitor's energy density. For example, capacitors are used in the power supply of cardiac defibrillators. A defibrillator is an implanted medical device that continuously monitors the performance of the patient's heart. When a "fibrillation", or heartbeat irregularity is detected, the device delivers a high voltage pulse to the heart via a lead connecting the defibrillator to the heart. This high voltage pulse usually restores the heart's normal rhythmic function. For a defibrillator to properly function, a special type of capacitor having a high energy density is required.
However, the size of the capacitor remains a problem. Current defibrillator capacitors are one of the larger components of a defibrillator. As a result, the defibrillator usually must be implanted in the patient's abdomen--a less desirable location as compared to implantation in the chest. Implantation in the chest cavity would require shorter electrical leads thereby reducing cost and patient discomfort. To achieve the significant miniaturization desired to reduce the overall size of the defibrillator capacitor, the capacitor's energy density must be substantially increased. Presently known materials have not made such miniaturization possible.
High energy density potential and overall component weight reduction may be important, even when miniaturization is not an issue for a particular application. Electric vehicles, for example, must incorporate capacitors capable of high energy density to provide bursts of power for acceleration or climbing, while desirably having reduced weight.
For a capacitor to work effectively, the dielectric layer must not transfer the stored charge prematurely. Therefore the dielectric layer must have low leakage current or high resistivity. In addition, the layer must not undergo dielectric breakdown in the presence of operating voltages. High voltage holdoff is difficult to accomplish if the dielectric material is made too thin. Voltage holdoff is understood to refer to the amount of voltage a material may "hold off" before breakdown occurs. On the other hand, a thick dielectric layer may also display poor (low) breakdown strength due to a greater tendency for imperfections in the dielectric layer as the layer thickness increases.
Many diamond-like coatings (DLCs) have been tried as dielectric materials in capacitors, but have failed for a variety of inherent structural reasons. One critical property of a successful dielectric capacitor material is superior long term adherence. Known DLCs do not possess satisfactory adherence on their own. Most known DLCs exhibit high intrinsic stress and inadequate adhesion. They also suffer from the presence of graphitic domains which lower resistivity, increasing leakage current. DLCs have low thermal stability, and rapidly graphitize at relatively low temperatures. Upon graphitization, the DLCs becomes conductive, thereby frustrating the purpose for the dielectric coating as a capacitor, rendering it useless. Such an event would be catastrophic for a capacitor sealed in an electrical implanted medical device, such as a fibrillator.
The lack of an adequately coated and insulated electrical component often results in the failure or shorter lifetime of the device served by the component. Further, radiation effects, including ultraviolet radiation and ion-bombardment often accelerate DLC deterioration through erosion or graphitization of the DLC coating.
A strong, highly adherent, dielectric material which could be electrically "tuned" to increase its usefulness and flexibility as a capacitor, while also being deposited in ultra-thin layers and exhibiting outstanding high breakdown strength and high energy density would be desirable.